An example of a conventional internal batch mixer is disclosed in the following Patent Literature 1. In an internal batch mixer of Patent Literature 1, a mixing chamber is formed inside a casing, and mixing rotors are disposed within the mixing chamber. The casing includes a discharge opening formed to extend in the axial direction of the mixing rotor, and a drop door provided to open and close the discharge opening. The drop door prevents outflow of a material by blocking the discharge opening during mixing of the material within the mixing chamber. When the material mixed in the mixing chamber is discharged, the drop door is rotated and opened downwardly.
This internal batch mixer further includes a latch device that is a lock mechanism for the drop door. The latch device includes a latch and a hydraulic cylinder. The latch is installed to move forward and backward so as to slide relative to the drop door. The drop door is locked by pressing a contact surface of the latch onto a contact surface of the drop door by the hydraulic cylinder, and the airtightness within the mixing chamber is consequently maintained. When the latch is retracted, the drop door becomes openable.
In a conventional apparatus as described above, repetitive opening and closing operation of the drop door causes wear at a contact area between the drop door and the latch. For example, the wear is caused on a contact plate of the door on the door side and on a latch striker of the latch on the latch side. Therefore, in the past, a wear status for contact parts (consumable parts) has been visually confirmed by dispatching a worker to a place where the latch device can be viewed.
The conventional visual confirmation of wear status for the contact parts has been performed also by installing a scale plate on a base part of the mixer, attaching a landmark member to a piston rod of the hydraulic cylinder, and comparing a position of the landmark member with a scale of the scale plate.
Accordingly, confirmation of wear status for a component or as-needed replacement of the component requires the reading operation of the scale or the position readjustment operation of the scale plate.
However, since the hydraulic cylinder is generally in a location distant from the work area of a mixer's operator during mixing operation, it is troublesome for the operator to perform the above-mentioned confirmation during the mixing operation. Further, since the scale plate is generally covered with a dust collecting cover or the like, the confirmation operation or the readjustment operation is not easy. The dust collecting cover may be provided with a switch of a safety device. In this case, it is difficult to perform the above-mentioned confirmation operation during the operation of the mixer since the mixer is shut down when the dust collecting cover is opened during the operation.
Even if the above-mentioned confirmation operation or readjustment operation is possible from the viewpoint of machine structure, the confirmation operation is difficult just the same since the scale plate is contaminated in a work environment which needs dust collection. Therefore, it is common to perform the above-mentioned confirmation operation while the operation of the mixer is stopped.
The confirmation of the wear status, or the confirmation of the scale plate or the like, can be delayed depending on the operation cycle of the mixer. If the wear of the contact part is left in the meantime, damage on machine components such as deformation of a thin portion at the edge of the discharge opening, that is to contact with the drop door in the casing, is caused when the latch mechanism is, for example, of toggle type. When the latch mechanism is of slide type, also, the wear is similarly caused in the contact area between the door and the latch. If the replacement time of contact part is missed, the casing or the like that is a durable component is also damaged. Since it is generally difficult to continuously grasp the wear status with respect to such a contact part in the latch mechanism, the replacement time thereof can be hardly predicted. In this way, neglect of the wear status in the contact area causes damages on machine components in both the toggle type and the slide type of latch mechanisms.
As described above, in the latch device of the conventional internal batch mixer, it is difficult to grasp the wear status of mutual contact portions of the door and the latch member, which are wearing members.
The following Patent Literature 2 discloses an internal batch mixer provided with a seal mechanism. The seal mechanism prevents mixing material within a mixing chamber from leaking out of the mixing chamber from an area in the vicinity of an end portion of a mixing rotor within the mixing chamber.
This seal mechanism includes a seal member which prevents the leak of mixing material out of the mixing chamber by being pressed onto the end portion of the rotor in the axial direction of the rotor. The seal member is composed of a rotation-side seal member fixed to an end surface of the rotor, and a fixed-side seal member fixed to an end surface of a dust stop ring through which the rotor shaft is inserted. These rotation-side seal member and fixed-side seal member are consumable members which are worn away through mutual sliding. In Patent Literature 2, one of these seal members is formed by use of a material consisting of a resin compound filled with graphite or short carbon fiber not more than ½ inch in fiber length. This allows a reduced value of friction coefficient of the sliding surfaces of both the seal members to suppress the heat generation or wear of both the seal members that are consumable members.
One of techniques relating to the seal mechanism for internal batch mixer is described in the following Patent Literature 3. In the technique described in Patent Literature 3, the heat generation or wear of the seal members is suppressed by rotating a first sleeve having a frictional wearing member fixed to an end surface thereof, which corresponds to the above-mentioned fixed-side seal member, in a rotor rotating direction at a rotating speed lower than the rotating speed of the rotor shaft, thereby reducing the mutual sliding speed of the seal members.
Another technique relating to the seal mechanism is also described in the following Patent Literature 4. In the technique described in Patent Literature 4, internal pressure of the mixing chamber is measured, and seal pressure, or biasing force of a seal ring to a collar ring, is appropriately adjusted in response to the measured value of pressure by an adjustment means having a hydraulic cylinder. When the mixing chamber is low in internal pressure at the terminal stage of mixing process or the like, the life of the seal members can be extended by reducing the seal pressure.
Each of the techniques descried in Patent Literatures 2 to 4 is intended to extend the life of seal members that are consumable members by preventing the wear of the seal members. However, these seal members are consistently consumable members. Therefore, these seal members wear down little by little, and reach the end of their lives at some stage. In other words, the seal members are members which reach their application limits at some stage. On the other hand, the operator hardly confirm sliding seal portions of the seal members during the mixing operation of the mixer since the position of the seal members is distant from the operator's work area during the operation. For grasping the abrasion loss of the seal members, further, the operator must confirm a depth of wear as small as several mm. Moreover, it is difficult to confirm the abrasion loss of the seal members based on a machined part around the seal members since machined parts are fewer around the seal members in the mixer. Even if the abrasion loss of the seal portion is to be measured based on the machined part, it is substantially impossible to carry out this measurement during mixing operation. From these reasons, it often happens that a countermeasure such as replacement of seal member is taken once after dust of the mixing material begins to leak through the seal portion.
When the dust of the mixing material begins to leak through the seal portion, breakage of piping or a temperature sensor in the vicinity of the leaked mixing material is also feared in addition to damages on counter members of the mutually-sliding sliding surfaces. The breakage of the piping or temperature sensor results in further serious damage. Further, the leak of mixing material requires disposal of the leaked mixing material. A high leakage rate of the mixing material leads to deterioration of work efficiency due to the necessity of cleaning of the periphery of the mixer.
As described above, a technique for grasping the wear level of a seal member that is a wearing member in the conventional seal mechanism for internal batch mixer was needed.